Multilevel Inverter For Grid-Connected PV System Employing Digital PI Controller

This paper presents a single-phase five-level photovoltaic (PV) inverter topology for grid-connected PV systems with a novel pulsewidth-modulated (PWM) control scheme. Two reference signals identical to each other with an offset equivalent to the amplitude of the triangular carrier signal were used to generate PWM signals for the switches. A digital proportional-integral current control algorithm is implemented in DSP TMS320F2812 to keep the current injected into the grid sinusoidal and to have high dynamic performance with rapidly changing atmospheric conditions. The inverter offers much less total harmonic distortion and can operate at near-unity power factor. The proposed system is verified through simulation and is implemented in a prototype, and the experimental results are compared with that with the conventional single-phase three-level grid-connected PWM inverter.     

Intelligent PV Module for Grid-Connected PV Systems

Most issues carried out about building integrated photovoltaic (PV) system performance show average losses of about 20%–25% in electricity production. The causes are varied, e.g., mismatching losses, partial shadows, variations in current–voltage$(I$–$V)$characteristics of PV modules due to manufacturing processes, differences in the orientations and inclinations of solar surfaces, and temperature effects. These losses can be decreased by means of suitable electronics. This paper presents the intelligent PV module concept, a low-cost high-efficiency dc–dc converter with maximum power point tracking (MPPT) functions, control, and power line communications (PLC). In addition, this paper analyses the alternatives for the architecture of grid-connected PV systems: centralized, string, and modular topologies. The proposed system, i.e., the intelligent PV module, fits within this last group. Its principles of operation, as well as the topology of boost dc–dc converter, are analyzed. Besides, a comparison of MPPT methods is performed, which shows the best results for the incremental conductance method. Regarding communications, PLC in every PV module and its feasibility for grid-connected PV plants are considered and analyzed in this paper. After developing an intelligent PV module (with dc–dc converter) prototype, its optimal performance has been experimentally confirmed by means of the PV system test platform. This paper describes this powerful tool especially designed to evaluate all kinds of PV systems.     

A New Simplified Multilevel Inverter Topology for DC–AC Conversion

Multilevel converters offer high power capability, associated with lower output harmonics and lower commutation losses. Their main disadvantage is their complexity, requiring a great number of power devices and passive components, and a rather complex control circuitry. This work reports a new multilevel inverter topology using an H-bridge output stage with a bidirectional auxiliary switch. The new topology produces a significant reduction in the number of power devices and capacitors required to implement a multilevel output. The new topology is used in the design of a five-level inverter; only five controlled switches, eight diodes, and two capacitors are required to implement the five-level inverter using the proposed topology. The new topology achieves a 37.5% reduction in the number of main power switches required (five in the new against eight in any of the other three configurations) and uses no more diodes or capacitors that the second best topology in the literature, the Asymmetric Cascade configuration. Additionally, the dedicated modulator circuit required for multilevel inverter operation is implemented using a FPGA circuit, reducing overall system cost and complexity. Theoretical predictions are validated using simulation in SPICE, and satisfactory circuit operation is proved with experimental tests performed on a laboratory prototype.     

光伏并网系统反孤岛控制策略研究

随着分布式供电系统的逐步发展,反孤岛控制已成为并网供电中不可缺少的环节。文中结合光伏并网逆变器的控制过程介绍了几种传统的反孤岛方法,分析了这些方法中的检测盲区,详细介绍了正反馈频率法的控制原理和控制过程,并给出程序控制流程图,运用Matlab对该方法进行了仿真。仿真结果表明该方法能够快速地检测出孤岛的发生并断开逆变器与电网的连接,无检测盲区,对孤岛效应能够做到有效的防范。     

Electrical PV Array Reconfiguration Strategy for Energy Extraction Improvement in Grid-Connected PV Systems

This paper applies a dynamical electrical array reconfiguration (EAR) strategy on the photovoltaic (PV) generator of a grid-connected PV system based on a plant-oriented configuration, in order to improve its energy production when the operating conditions of the solar panels are different. The EAR strategy is carried out by inserting a controllable switching matrix between the PV generator and the central inverter, which allows the electrical reconnection of the available PV modules. As a result, the PV system exhibits a self-capacity for real-time adaptation to the PV generator external operating conditions and improves the energy extraction of the system. Experimental results are provided to validate the proposed approach.     

Multilevel Inverter Topologies for Stand-Alone PV Systems

This paper shows that versatile stand-alone photovoltaic (PV) systems still demand on at least one battery inverter with improved characteristics of robustness and efficiency, which can be achieved using multilevel topologies. A compilation of the most common topologies of multilevel converters is presented, and it shows which ones are best suitable to implement inverters for stand-alone applications in the range of a few kilowatts. As an example, a prototype of 3 kVA was implemented, and peak efficiency of 96.0% was achieved.     

Wavelet-Based Islanding Detection in Grid-Connected PV Systems

Distributed power generation systems (DPGSs) based on inverters require reliable islanding detection algorithms (passive or active) in order to determine the electrical grid status and operate the grid-connected inverter properly. These methods are based on the analysis of the DPGS voltage, current, and power in time or frequency domain. This paper proposes a time-frequency detection algorithm based on monitoring the DPGS output power considering the influence of the pulsewidth modulation, the output LCL filter, and the employed current controller. Wavelet analysis is applied to obtain time localization of the islanding condition. Simulation and experimental results show the performance of the proposed detection algorithm in comparison with existing methods.     

新兴应用给数据转换提出新要求

新一级别的高性能、小外形、低功耗数据转换器为大多数重要的工业、医疗以及通信等应用提供了特别需要的高速响应、多信道以及低延迟等性能.     

Energy-Balance Modeling and Discrete Control for Single-Phase Grid-Connected PV Central Inverters

This paper presents a two-control loop design considering the nonlinear time-varying characteristics of a single-phase grid-connected photovoltaic (PV) full-bridge central inverter. The control scheme design is based on the energy-balance modeling of the PV system and enables the design of a voltage loop linear discrete controller ensuring the stability of the system for the whole range of PV array operating conditions. A set of experimental results carried out on a laboratory prototype is provided to validate the proposed approach.     

The AC Line Current Regulation Strategy for the Grid-Connected PV System

The ac line current regulation strategy for the grid-connected photovoltaic (GCPV) system is proposed in this paper. The power flow of the GCPV system and the operational principles of different ac line current regulation strategies are presented. In this paper, the optimal ac line current regulation is defined to be able to achieve dc-link voltage regulation in one 60 Hz ac mains cycle while minimizing the injected ac line current variation. The mathematical equations for the proposed optimal ac line current regulation strategy are derived thoroughly. The derived equations also explain the behavior of the dc-link voltage responding to the power variation of the GCPV system. As a result, the selection criteria of the dc-link capacitor can be established. Hardware experimental results have been presented to verify the validity of the proposed optimal ac line current regulation strategy.      

双级式单相光伏并网系统的研究与仿真

介绍了双级式单相光伏并网系统,分析了其拓扑结构。升压采用模糊推理进行最大功率点跟踪控制;双闭环控制实现了对电网电压的同频同相控制,达到了并网要求。通过MatlabR2010对系统进行了仿真,仿真结果表明逆变输出电流和电网电压同频同相,并有效地跟踪了光伏阵列的最大功率点。     

基于重复控制算法的光伏并网逆变器的研究

本文介绍了一种基于重复控制算法的光伏并网逆变器系统。该控制算法对死区影响及其它周期性扰动有明显的抑制作用,而且能消除跟踪误差,使系统输出达到无静差。同时,在控制中还将前馈控制与重复控制相结合,克服了重复控制固有的滞后调节特性,改善了光伏并网逆变器的输出并网电流波形和稳态误差。     

基于XC164CM的光伏并网发电系统

并网发电系统是太阳能利用的主流趋势,而高性能数字信号处理器的发展也使得一些先进复杂的控制策略应用于光伏并网系统成为可能。文中对系统的控制方案进行了分析,并采用英飞凌公司生产的XC164CM作为系统的控制芯片,通过软件编程完成了系统的并网控制,并解决了最大功率点跟踪、锁相环等关键问题。实验表明文中设计的光伏并网发电系统能够较好地实现逆变并网功能。     

基于DSP的光伏逆变并网的同步控制

文章介绍了光伏并网逆变器的基本原理,通过无差拍PWM控制方式来实现逆变电流快速跟踪电网电流。给出了基于DSP的三相光伏并网逆变器的软硬件设计方案和实验结果。实验结果说明了DSP在光伏发电方面具有广阔的应用前景。     

Control of a Single-Phase Cascaded H-Bridge Multilevel Inverter for Grid-Connected Photovoltaic Systems

This paper presents a single-phase cascaded H-bridge converter for a grid-connected photovoltaic (PV) application. The multilevel topology consists of several H-bridge cells connected in series, each one connected to a string of PV modules. The adopted control scheme permits the independent control of each dc-link voltage, enabling, in this way, the tracking of the maximum power point for each string of PV panels. Additionally, low-ripple sinusoidal-current waveforms are generated with almost unity power factor. The topology offers other advantages such as the operation at lower switching frequency or lower current ripple compared to standard two-level topologies. Simulation and experimental results are presented for different operating conditions.     

Grid-Connected Photovoltaic Multistring PCS With PV Current Variation Reduction Control

In this paper, a grid-connected photovoltaic (PV) multistring power conditioning system with PV input current reduction control is proposed. An improved maximum power point tracking (MPPT) method for the multistring converter is suggested. The suggested MPPT algorithm tracks the maximum power point even though measurement errors exist. To reduce the PV current variation introduced by the inverter, a PV current variation reduction control is suggested. This PV current variation reduction control reduces the PV current variation without additional components. The low current variation reduces the filter size and improves the MPPT efficiency. All algorithms and controllers are implemented on a single-chip microcontroller. Experimental results obtained on a 3-kW prototype show high performance such as a MPPT efficiency of 99.7%, an almost unity power factor, a power efficiency of 96.7%, and a total harmonic distortion of 2.0%.     

大功率光伏并网逆变器控制系统分析与实现

文章深入分析了大功率光伏并网逆变器的控制系统。介绍了光伏并网逆变器的分类,以及大功率光伏并网逆变器的电路拓扑;重点分析了最大功率跟踪MPPT、功率因数调节、锁相、孤岛检测、低电压穿越等关键技术。应用这些关键技术设计的500 kW光伏并网逆变器,具有变换效率高、MPPT范围宽、并网电流失真度小、功率因数高、体积重量小、成本低等优点。     

Design Strategy to Optimize the Reliability of Grid-Connected PV Systems

This paper presents a strategy, based on the design-of-experiments technique, aimed at optimizing the reliability in inverters for photovoltaic systems. The process involves designing the inverter several times, each time with different specifications, and calculating the reliability for each design. The specifications are established in a systematic manner, in such a way that the parameters with the highest impact are easily identified. The optimization procedure follows a standard reliability estimation methodology and involves modifying the stress factors in a judicious manner. The strategy is exemplified with an integrated boost inverter and a desired mean time between failures of 12 years.